This application claims priority to an application entitled xe2x80x9cDevice and Method for Generating Quaternary Complex Quasi-orthogonal Code in CDMA Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Sep. 8, 1998 and assigned Serial No. 98-37453, as well as an application filed in the Korean Industrial Property Office on Dec. 9, 1998, and assigned Serial No. 98-54569; the contents of both are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a coding device and method for a mobile communication system, and in particular, to a device and method for generating quaternary complex quasi-orthogonal codes and then using those generated quaternary complex quasi-orthogonal codes to generate spreading channel signals.
2. Description of the Related Art
In general, a CDMA (Code Division Multiple Access) mobile communication system performs channel separation using orthogonal codes in order to increase channel capacity. For example, a forward link specified by the IS-95/IS-95A standard separates the channels using the orthogonal codes. This channel separation method can also be applied to a reverse link through time alignment.
FIG. 1 illustrates the IS-95/IS-95A forward link in which channels are separated by orthogonal codes. Referring to FIG. 1, channels are separated by associated orthogonal codes Wi (where i=0 to 63), respectively, which typically are Walsh codes. The IS-95/IS-95A forward link uses convolutional codes having a code rate R=1/2, employs BPSK (Binary Phase Shift Keying) modulation, and has a bandwidth of 1.2288 MHz. Accordingly, the number of available channels is 1.2288 MHz/(9.6 KHz*2)=64. That is, the IS-95/IS-95A forward link can separate channels using 64 Walsh codes.
As stated above, the number of available orthogonal codes depends on the employed modulation method and the minimum data rate. However, in future CDMA mobile communication systems, channels assigned to the users will increase in number in order to improve performance. To this end, future CDMA mobile communication systems will need to increase the channel capacity of traffic channels, pilot channels and control channels.
However, there are a limited number of available orthogonal codes the improved system can use. Therefore, any increase in channel capacity will be restricted due to the limitation on the number of available orthogonal codes. To solve this problem, it is desirable to generate quasi-orthogonal codes, which will have the least interference with the orthogonal codes and a variable data rate.
It is, therefore, an object of the present invention to provide a device and method for generating quasi-orthogonal code masks for generating quaternary complex quasi-orthogonal codes which have the least interference with orthogonal codes being used in a CDMA communication system.
It is another object of the present invention to provide a device and method for generating quasi-orthogonal codes for channel separation using quasi-orthogonal code masks and Walsh orthogonal codes in a QPSK (Quaternary Phase Shift Keying) CDMA communication system.
It is a further object of the present invention to provide a device and method for spreading channel signals using quaternary complex quasi-orthogonal codes in a CDMA communication system.
It is still another object of the present invention to provide a device and method for generating quasi-orthogonal code masks for generating quaternary complex quasi-orthogonal codes, selecting one of the quasi-orthogonal code masks to generate quasi-orthogonal codes and spreading channel signals to be transmitted using the generated quasi-orthogonal codes.
In one embodiment of the present invention, a method for generating a quaternary complex quasi-orthogonal code in a CDMA communication system comprises generating an M-sequence and specific sequences having the same length and a good full correlation property with the M-sequence; generating candidate masks by column permutation, in the same manner as a column permutation that converts the M-sequence to a Walsh code, of specific sequences; generating quasi-orthogonal code representatives by operating the candidate masks and Walsh codes having the same length as that of the candidate masks; and selecting a quasi-orthogonal code satisfying a partial correlation with the Walsh codes, out of the generated quasi-orthogonal code representatives, and selecting a mask related to generation of the selected quasi-orthogonal code.
In another embodiment of the present invention, a channel transmission device for a CDMA communication system comprises a complex signal converter for converting a channel coded signal to a complex signal; a generator including a quaternary complex quasi-orthogonal code mask, for generating a quaternary complex quasi-orthogonal code by operating the quaternary complex quasi-orthogonal code mask to a Walsh code; a channel spreader for generating a channel spread signal by operating the converted complex signal and the quaternary complex quasi-orthogonal code; and a PN masking part for generating a PN masked channel signal by operating the channel spread complex signal and complex PN sequence.